Many consumer electronics products include at least one camera. These include tablet computers, mobile phones, and smart watches. In such products, and in digital still cameras themselves, high-dynamic range (HDR) functionality enables consumers to produces images of scenes having a larger dynamic range of luminosity than with cameras lacking such functionality.
For example, FIG. 1 depicts a camera 130 imaging a scene 120 having a high dynamic range of luminance. Scene 120 includes a person 121 in front of a window 122, through which a sunny scene 123 is visible. Camera 130 includes an imaging lens (not shown), an image sensor 132, a memory 110, and a microprocessor 140 communicatively coupled to the image sensor. Image sensor 132 includes a pixel array 134A and may include a color filter array (CFA) 136 thereon. Pixel array 134A includes a plurality of pixels 134, not shown in FIG. 1 for clarity of illustration. Each color filter of CFA 136 is aligned with a respective pixel 134 of pixel array 134A. The imaging lens images scene 120 onto image sensor 132. Image sensor 132 also includes circuitry 138 that includes at least one analog-to-digital converter.
Indoor lighting, not shown, illuminates the front of person 121 facing the camera, while sunlight illuminates sunny scene 123. In scene 120, person 121 and sunny scene 123 have respective luminosities 121L and 123L, not shown in FIG. 1. Since the sunlight is significantly brighter than the indoor lighting, luminosity 123L far exceeds luminosity 121L such that scene 120 has a high dynamic range of luminosity. Standard digital imaging enables capture of scene 120 using a single exposure time optimized for either luminosity 121L or 123L. When the exposure time is optimized for luminosity 121L, person 121 is properly exposed while sunny scene 123 is overexposed. When the exposure time is optimized for luminosity 123L, sunny scene 123 is properly exposed while person 121 is underexposed.
With HDR imaging, camera 130 captures multiple images, each with a different exposure time, of scene 120 and stores them in memory 110. Microprocessor 140 processes the multiple images to form a composite HDR image 190. HDR images are prone to image artifacts resulting from movement, between capture of the multiple images, of either objects in scene 120 or of camera 130. The artifacts, known as “ghosts,” appear as semi-transparent images of the moving object trailing behind the moving object. For example, HDR image 190 includes ghost artifacts 194 of the right hand of person 121.